Q.f - Greenhouse Effect & GHG Sources

f 6 Marks

What is green house effect? Discuss about the major sources of green house gases.

Answer: Greenhouse Effect and Sources of GHGs

1. What is Greenhouse Effect?

Greenhouse Effect is the natural process by which certain gases in Earth's atmosphere trap infrared radiation (heat) emitted from the Earth's surface, warming the lower atmosphere and maintaining temperatures suitable for life. Without this effect, Earth's average temperature would be about -18°C instead of +15°C.

Mechanism:

Step 1: Sun emits short-wave solar radiation (visible light, UV) that passes through atmosphere
Step 2: Earth's surface absorbs this radiation and heats up
Step 3: Earth re-emits energy as long-wave infrared (heat) radiation
Step 4: Greenhouse gases absorb this infrared radiation
Step 5: GHGs re-emit radiation in all directions, including back to Earth's surface
Result: Lower atmosphere warms up (like a greenhouse trapping heat)

Natural vs Enhanced Greenhouse Effect:

Natural: Essential for life; maintains habitable temperatures
Enhanced: Human activities increase GHG concentrations, trapping more heat and causing global warming

Key Point: The problem is not the greenhouse effect itself (which is essential), but the ENHANCED greenhouse effect caused by human-generated emissions that intensify warming beyond natural levels.

2. Major Greenhouse Gases and Their Sources

A. Carbon Dioxide (CO2) - 76% of warming

Source	Contribution	Details
Fossil Fuel Combustion	~75%	Coal, oil, gas for power, transport, industry
Deforestation	~10%	Forest clearing releases stored carbon
Industrial Processes	~5%	Cement, steel production
Other	~10%	Land use, agriculture, waste

B. Methane (CH4) - 16% of warming, GWP = 28-36

Agriculture: Livestock digestion (enteric fermentation), rice paddies (40%)
Fossil Fuels: Natural gas leaks, coal mining, oil extraction (35%)
Waste: Landfills, wastewater treatment (20%)
Natural: Wetlands, termites (minor human influence)

C. Nitrous Oxide (N2O) - 6% of warming, GWP = 265-298

Agriculture: Nitrogen fertilizers, manure (60%)
Industry: Nitric acid, adipic acid production (20%)
Combustion: Fossil fuels, biomass burning (10%)
Other: Wastewater, natural soil processes

D. Fluorinated Gases (F-gases) - 2% of warming, Very High GWP

Gas Type	Sources	GWP
HFCs	Refrigeration, air conditioning, aerosols	12-14,800
PFCs	Aluminum production, semiconductors	7,390-12,200
SF6	Electrical switchgear, magnesium production	23,500
NF3	Electronics manufacturing	17,200

E. Water Vapor (H2O)

Most abundant GHG but acts as feedback, not driver
Concentration depends on temperature; not directly controlled
Amplifies warming: warmer air holds more moisture, increasing effect

3. Sectoral Breakdown of Global GHG Emissions

Sector	Share	Main Gases
Energy (Electricity, Heat)	25%	CO2
Agriculture, Forestry, Land Use	24%	CO2, CH4, N2O
Industry	21%	CO2, F-gases
Transportation	14%	CO2
Buildings	6%	CO2
Other Energy	10%	CO2, CH4

4. Current Atmospheric Concentrations

CO2: ~420 ppm (pre-industrial: 280 ppm) - 50% increase
CH4: ~1,900 ppb (pre-industrial: 700 ppb) - 170% increase
N2O: ~335 ppb (pre-industrial: 270 ppb) - 24% increase

Conclusion

The greenhouse effect is a natural phenomenon essential for life on Earth, maintaining surface temperatures about 33°C warmer than they would otherwise be. However, human activities - particularly fossil fuel combustion, deforestation, agriculture, and industrial processes - have dramatically increased GHG concentrations, enhancing the greenhouse effect and causing global warming. CO2 from fossil fuels is the dominant contributor, but methane and nitrous oxide from agriculture and waste, along with synthetic F-gases, also play significant roles. Understanding these sources is essential for developing targeted mitigation strategies across all sectors.

Sources: Module 1 Notes | IPCC AR6 | NOAA | EPA